| Message ID | 1447260696-450-5-git-send-email-stefano.stabellini@eu.citrix.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wednesday 11 November 2015 16:51:35 Stefano Stabellini wrote: > +static void xen_read_wallclock(struct timespec64 *ts) > +{ > + u32 version; > + u64 delta; > + struct timespec64 now; > + struct shared_info *s = HYPERVISOR_shared_info; > + struct pvclock_wall_clock *wall_clock = &(s->wc); > + > + /* get wallclock at system boot */ > + do { > + version = wall_clock->version; > + rmb(); /* fetch version before time */ > + now.tv_sec = ((uint64_t)wall_clock->sec_hi << 32) | wall_clock->sec; > + now.tv_nsec = wall_clock->nsec; > + rmb(); /* fetch time before checking version */ > + } while ((wall_clock->version & 1) || (version != wall_clock->version)); > + > + /* time since system boot */ > + delta = ktime_get_ns(); > + delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec; > + > + *ts = ns_to_timespec64(delta); > +} Looks correct to me and better than the previous versions, but you are still converting from timespec64 to nanoseconds and back. While I previously recommended going all the way to nanoseconds here, I guess this you can even avoid the ns_to_timespec64() if you stay within timespec64 domain and replace the last lines with ktime_get_ts64(&ts_monotonic); *ts = timespec64_add(now, ts_monotonic); which avoids both the multiplication and division. Arnd
On Wed, 11 Nov 2015, Arnd Bergmann wrote: > On Wednesday 11 November 2015 16:51:35 Stefano Stabellini wrote: > > +static void xen_read_wallclock(struct timespec64 *ts) > > +{ > > + u32 version; > > + u64 delta; > > + struct timespec64 now; > > + struct shared_info *s = HYPERVISOR_shared_info; > > + struct pvclock_wall_clock *wall_clock = &(s->wc); > > + > > + /* get wallclock at system boot */ > > + do { > > + version = wall_clock->version; > > + rmb(); /* fetch version before time */ > > + now.tv_sec = ((uint64_t)wall_clock->sec_hi << 32) | wall_clock->sec; > > + now.tv_nsec = wall_clock->nsec; > > + rmb(); /* fetch time before checking version */ > > + } while ((wall_clock->version & 1) || (version != wall_clock->version)); > > + > > + /* time since system boot */ > > + delta = ktime_get_ns(); > > + delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec; > > + > > + *ts = ns_to_timespec64(delta); > > +} > > Looks correct to me and better than the previous versions, but you are still > converting from timespec64 to nanoseconds and back. While I previously > recommended going all the way to nanoseconds here, I guess this you > can even avoid the ns_to_timespec64() if you stay within timespec64 > domain and replace the last lines with > > ktime_get_ts64(&ts_monotonic); > *ts = timespec64_add(now, ts_monotonic); > > which avoids both the multiplication and division. Much better, I'll do that. Thanks for the suggestion!
diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c index 2f57ba3..eede8e9 100644 --- a/arch/arm/xen/enlighten.c +++ b/arch/arm/xen/enlighten.c @@ -28,6 +28,7 @@ #include <linux/cpufreq.h> #include <linux/cpu.h> #include <linux/console.h> +#include <linux/timekeeping.h> #include <linux/mm.h> @@ -95,6 +96,30 @@ static unsigned long long xen_stolen_accounting(int cpu) return state.time[RUNSTATE_runnable] + state.time[RUNSTATE_offline]; } +static void xen_read_wallclock(struct timespec64 *ts) +{ + u32 version; + u64 delta; + struct timespec64 now; + struct shared_info *s = HYPERVISOR_shared_info; + struct pvclock_wall_clock *wall_clock = &(s->wc); + + /* get wallclock at system boot */ + do { + version = wall_clock->version; + rmb(); /* fetch version before time */ + now.tv_sec = ((uint64_t)wall_clock->sec_hi << 32) | wall_clock->sec; + now.tv_nsec = wall_clock->nsec; + rmb(); /* fetch time before checking version */ + } while ((wall_clock->version & 1) || (version != wall_clock->version)); + + /* time since system boot */ + delta = ktime_get_ns(); + delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec; + + *ts = ns_to_timespec64(delta); +} + static void xen_percpu_init(void) { struct vcpu_register_vcpu_info info; @@ -303,6 +328,11 @@ static int __init xen_pm_init(void) pm_power_off = xen_power_off; arm_pm_restart = xen_restart; + if (!xen_initial_domain()) { + struct timespec64 ts; + xen_read_wallclock(&ts); + do_settimeofday64(&ts); + } return 0; }
Read the wallclock from the shared info page at boot time. Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com> --- Changes in v3: - use ktime_get_ns instead of calling into the arch_timer functions directly - read the wallclock from the late_initcall Changes in v2: - properly convert arch_timer ticker to nsec - use timespec64 interfaces - use sec_hi to get a 64-bit seconds value --- arch/arm/xen/enlighten.c | 30 ++++++++++++++++++++++++++++++ 1 file changed, 30 insertions(+)